Albert Barnes Commentary 2 Samuel 12:8

"and I gave thee thy master`s house, and thy master`s wives into thy bosom, and gave thee the house of Israel and of Judah; and if that had been too little, I would have added unto thee such and such things." — 2 Samuel 12:8 (ASV)

And your master’s wives ... - According to Eastern custom, the royal harem was a part of the royal inheritance. The prophets spoke in such matters according to the received opinions of their day, and not always according to the abstract rule of right .